The instant invention relates to the machine tool art and more particularly to a machining apparatus comprising an improved workpiece holding assembly for holding and positioning a workpiece during a machining operation and to the improved workpiece holding assembly per se.
Machining apparatus such as precision surface and profile grinding machines, milling machines and other surface cutting machines have been well known in the machine tool industry for many years. In this connection, a typical conventional machining apparatus of this general type includes a chuck for holding a workpiece during a machining operation, a cutting tool which is engageable with the work piece for performing a machining operation thereon, and means for effecting relative movement between the cutting tool and the workpiece during the machining operation in order to generate a desired surface configuration in the workpiece. Generally, the means for effecting relative movement between a cutting tool and a workpiece in a machining apparatus of this type is operative for effecting relative movement in each of three mutually perpendicular directions during a machining operation in order to produce a desired surface configuration in the workpiece. In addition, in some cases a machining apparatus of this type may further include a computerized numerical control for controlling the means for effecting relative movement between the workpiece and the cutting tool in each of the three directions in order to enable the machining apparatus to automatically generate a desired configuration in a workpiece with a high degree of accuracy and precision. Precision surface and profile grinding machines, such as the Jung JF 520 CNC and the Jung JF 625 CNC machines, are exemplary of automated machining apparatus of this general type and are currently available from K Jung GmbH, Jahnstrasse 80, Postfach 640, D-7320 Goppingen, West Germany. It will be understood, however, that a variety of other manufacturers also currently produce machining apparatus of this general type.
While machining apparatus of the above described general type have been found to be effective for precisely forming workpieces into various predetermined configurations during machining operations, they have generally been found to be ineffective for producing certain types of undercut surface configurations in workpieces. For example, machining apparatus of the above described types have generally been ineffective for producing undercut areas, such as dovetail-shaped slots, in workpieces. In this connection, heretofore it has generally been possible to adapt machining apparatus of the above described type to produce undercut areas in workpieces by utilizing manually adjustable sine chucks for securing workpieces during machining operations. However, these devices have only been manually adjustable for tilting workpieces, and they have been tedious and time consuming to operate. The only alternative to utilizing sine chucks for generating undercut areas in workpieces has been to utilize projection profile grinding apparatus comprising manually tiltable grinding wheels. However, these devices have also only been manually adjustable, and therefore they have had the same basic disadvantages as the machining apparatus which have included sine chucks. In addition, it has generally been necessary to manually adjust both projection profile grinding machines and machines having sine chucks for each individual change in the angular configuration of an undercut area. Hence, the procedures which have heretofore been required for forming undercut areas in workpieces have been extremely time consuming and tedious. Further, the potential for error has been relatively high in these procedures.
The instant invention effectively overcomes the problem of producing unusual surface configurations, such as undercut areas including dovetail-shaped slots, in workpieces with machining apparatus of the above described type. Specifically, the instant invention provides an improved workpiece holding assembly for a machining apparatus which is operable for securing and positioning a workpiece in a machining apparatus so that it can be presented to the cutting tool of the apparatus in various different angular positions. More specifically, the instant invention relates to an automatically tiltable workpiece holding assembly for a machining apparatus of the above described type and to the workpiece holding assembly as it is used in combination with a machining apparatus. The workpiece holding assembly generally comprises a base which is securable on a machining apparatus, an elongated gimble having a longitudinally extending tilt axis and mounted on the base so that it is rotatable about the tilt axis, means for automatically rotating the gimble about its tilt axis, and means for sensing the rotated position of the gimble with respect to its tilt axis. The base of the workpiece holding assembly is constructed so that when it is secured on a machining apparatus the tilt axis of the gimble extends in substantially parallel relation to one of the three mutually perpendicular directions of movement of the machining apparatus. Although the workpiece holding assembly can be effectively utilized with noncomputerized machining apparatus, it is preferably utilized with a machining apparatus having a computerized numerical control. Hence, preferably both the means for automatically rotating the gimble and the means for sensing the rotated position of the gimble are adapted to be interconnected with a computerized numerical control of a computerized machining apparatus for controlling the means for automatically rotating the gimble and the workpiece during a machining operation. In any event, when the workpiece holding assembly is installed in a machining apparatus of the above described type, regardless of whether or not the apparatus has a computer control, it adds a new dimension of relative movement between the workpiece and the cutting tool of the machining apparatus to enable the cutting tool to produce unusual surface configurations in the workpiece, such as undercut areas and slots.
In the preferred embodiment of the workpiece holding assembly of the instant invention, the means for rotating the gimble in the base comprises first and second worm gears on the gimble and first and second worm shafts which are rotatably mounted in the base. When the workpiece holding assembly is embodied in this manner, the first worm gear is operable for rotating the first worm shaft, whereas the second worm gear is operable for rotating the second worm shaft. Further, the first worm gear and the first worm shaft are constructed so that they are of opposite rotations from the second worm gear and the second worm shaft, and the first and second worm shafts are connected so that they rotate together but in opposite directions. Further, the worm shafts are adjusted so that when they are rotated to rotate the gimble, the first and second worm shafts simultaneously engage oppositely facing teeth of their respective worm gears to substantially prevent backlash movement in the gears which rotate the gimble. Further, the gimble is preferably supported in the base adjacent opposite longitudinal ends of the gimble, and the worm gears are preferably disposed in closely adjacent relation in a substantially central portion in the longitudinal extent of the gimble. The means for securing a workpiece on the gimble is preferably operable for securing the workpiece so that it is also positioned in the central portion of the gimble and in closely adjacent relation to the worm gears. As a result of these features, the workpiece holding assembly of the instant invention is operable for reorienting a workpiece with respect to a cutting tool in a highly accurate manner in order to produce precisely machined surface configurations in the work piece. In this connection, because the first and second worm gears are of opposite rotations and because the worm shafts engage oppositely facing teeth of the first and second worm gears, the looseness or backlash movement which would otherwise be inherent in a device of this type is substantially eliminated. Further, since the first and second worm gears are mounted on the gimble in closely adjacent relation to each other in a central portion of the gimble, the possibility of slightly deforming the gimble as a result of applying opposite torques thereto with the worm gears is essentially eliminated. Hence, it is possible to adjustably control the rotated position of a workpiece with a substantially higher degree of accuracy than was possible with the heretofore available machining apparatus and workpiece holding assemblies.
In the preferred application of the workpiece holding assembly of the subject invention, it is installed in a precision surface grinding machine of a type having a computerized numerical control and a rotating V-formed grinding wheel type cutting tool. The grinding machine is preferably further of a type wherein the first and second movement means are operable for moving the workpiece holding assembly in substantially perpendicular first and second directions, and wherein the third movement means is operable for moving the grinding wheel in a third direction which is mutually perpendicular to the first and second directions. The computerized numerical control of the apparatus may be either a point-to-point numerical control or a continuous-path numerical control, but in either case it is preferably operable for coordinating the rotational movement of the gimble in the workpiece holding assembly with the movement of the first, second and third movement means for presenting various portions of a workpiece to the grinding wheel in various different orientations. In this connection, it has been found that when the workpiece holding assembly of the subject invention is utilized in combination with a machining apparatus of this type, the machining apparatus can be effectively utilized for producing unusual surface configurations in workpieces, including undercuts such as dovetail slots, with extremely high degrees of precision. Further, the machining apparatus can be utilized for machining workpieces so that unusual surface configurations can be generated at substantially increased production rates.
Devices representing the closest prior art to the subjct invention of which the applicant is aware are disclosed in the U.S. patents to Mason U.S. Pat. No. 3,533,191; Hahn et al U.S. Pat. No. 3,634,976; Tokunaga et al U.S. Pat. No. 3,942,287; Verega U.S. Pat. No. 4,274,231; Enomoto et al U.S. Pat. No. 4,294,045; Oppelt et al U.S. Pat. No. 4,439,951; and Fletcher, Jr., et al U.S. Pat. No. 4,550,532. However, since none of these patents teach or suggest an effective device for automatically tilting a workpiece in the manner of the workpiece holding assembly of the subject invention, they are believed to be of only general interest.
Accordingly, it is a primary object of the instant invention to provide an automatically tiltable workpiece holding assembly for a machining apparatus.
Another object of the instant invention is to provide a machining apparatus which can be utilized for forming workpieces having undercut surface configurations with high degrees of accuracy at relatively high production rates.
Another object of the instant invention is to provide a tiltable workpiece holding assembly which is automatically tiltable through the use of a pair of worm gear assemblies having oppositely rotating worm shafts.
An even further object of the instant invention is to provide a tiltable workpiece holding assembly comprising a rotatable gimble and a pair of worm gear assemblies having oppositely rotating worm shafts wherein the worm gear assemblies are positioned in substantially central locations with respect to the longitudinal extent of the gimble to prevent twisting deformation in the gimble.